This application claims the priority of German patent document 10 2004 018 986.2, filed Apr. 20, 2004, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a method for generating a pulse signal having a definable pulse shape, using a multistage amplifier.
A report by Agilent Technologies Inc. entitled “Fundamentals of RF and Microwave Power Measurement (Part 1)” and dated Apr. 17, 2003, addresses the possibility that, in the case of multistage high-frequency transmitter amplifiers, a signal pulse generated by the transmitter amplifier may not have the desired pulse shape. An undesirable shape is exhibited particularly by a distorted course along the “top” (or upper edge) of the pulse, as illustrated, for example, in FIG. 1. In this particular example, it can be seen that the pulse exhibits a considerable overshoot at its leading edge, which is followed by a falling course. As a result of such undesirable pulse shapes the transmitted pulses can be detected only poorly.
Methods and circuits by means of which pulse-shaped signals with a definable pulse top are generated are known from German Patent Documents DE 30 23 861 A1, DE 43 39 191 A1, DE 29 04 011 B2 and DE 198 56 800 C1. However, these disclosures do not provide for pulse shaping over a wide dynamic range.
It is therefore an object of the invention to provide a method which permits generation of a pulse with a definable pulse shape over a high range of dynamics.
This and other objects and advantages are achieved by the method according to the invention, in which the course of the pulse top (upper edge) of the transmitted signal is determined by control signals at the amplifier stages. According to the invention, the latter control signals are definable such that, in each case, the control signal of an amplifier stage comprises a number of pulse sections of a definable frame pulse, with the course (upper edge) of each pulse section having a definable constant gradient. (That is, it comprises a straight line, with a constant slope.)
The method according to the invention carries out a type of predistortion for the pulse top. These predistortions are applied to all control signals of the respective desired amplifier stages, which advantageously are emitter-modulated amplifier stages. As a result of the “predistortion” introduced by the control signal, a transmitted output signal is generated which has the desired pulse shape along its top.
The frame pulse for an individual amplifier stage, with for example, a pulse duration of 32 μs, is advantageously digitally shaped and subsequently converted to an analog signal. According to the invention, the frame pulse comprises a freely selectable number of pulse sections. The application of individually formed frame pulses to the control signals for the respective amplifier stages achieves an optimal pulse course (shape) of the transmitted output pulse.
The individual pulse sections of the frame pulse advantageously have a (constant) negative or positive value-gradient. In this manner, it becomes possible to generate a predistortion that causes the pulse signal to be amplified in such a way that the transmitted output pulse signal follows precisely the desired pulse shape, including along its top edge, and undesirable pulse signal courses are eliminated.
The individual pulse sections of the frame pulse may have identical or different lengths.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.